Over the past few years, microfilm has seen increasing use as a medium of choice for compactly storing extremely large amounts of documentary information. Conventionally, this form of storage relies on photographically reducing the size of a page of a document by a substantial amount and then capturing an image of the reduced page on a corresponding frame of microfilm. Each such photographed page may depict a page in an individual business record, such as a completed business form or the like. Microfilm itself generally takes the form of a rolled transparent strip of developed film that typically contains thousands of successive substantially reduced images.
A microfilm image of a document rarely, if ever, exists by itself utterly devoid of identifying data. On the one hand, this data, in a manual microfilm retrieval system, consists of sufficient human readable text that identifies the range of images stored on that entire roll, e.g. issues of The New York Times for the years 1988-1990 or U.S. Pat. Nos. 4,955,000 through 4,958,000. This information is generally situated on an outer surface of a case for the roll. Unfortunately, the very limited space on the roll case often precludes the inclusion of any, let alone sufficient, text to describe each individual image in that roll. On the other hand, in an automated image management system, image identifying information would typically be stored on magnetic media in a user searchable computer database connected to an automated film library. Here, this information might consist of illustratively microfilm roll and frame numbers along with suitable pre-defined identifying criteria, such as various keywords or the like, that describes each stored microfilm image accessible through the system. Unfortunately, an automated image management system is frequently too expensive for use in many small and intermediate-sized microfilm based image storage applications.
Furthermore, microfilm has the inherent advantage that it does not deteriorate with time as quickly as does magnetic media. After several years of remaining in a static condition, magnetic media tends to rapidly deteriorate by experiencing drop-outs and/or other similar artifacts that adversely affect the integrity of data stored thereon. However, microfilm generally deteriorates much more slowly than magnetic media and therefore provides substantially greater long term data integrity than does magnetic media.
With the above considerations in mind, an overall need has arisen in the art to be able to store a reasonable, though limited, amount of digital data on microfilm co-extensively with a human readable image appearing thereon. By doing so, a significant amount of identifying information could be included with each microfilm image without, in many instances, the necessity to store this information in a computer and specifically in magnetic media associated therewith. As a result, a relatively low cost microfilm retrieval system could be constructed which would still provide significant amounts of identifying information for each stored image, clearly substantially more than that which would be available with a manual microfilm retrieval system of the type described above. Specifically, the information would be specific to the image and be read while the image is being scanned. This information could, for example, include identifying indicia for an associated image. Alternatively, if the image is a page of a microfilmed form, this data could be textual data that results from optically reading and digitizing various pre-defined fields in this page. This data, being stored in digital form, could easily be read into a computer for subsequent data processing as a result of the same scanning pass during which the image itself is being scanned and digitized for subsequent image processing. Alternatively, this data could merely be read and locally displayed as text to an operator in order to identify and/or describe a particular microfilm image that is then being displayed.
One technique which is well known in the art for storing digital data on non-magnetic media, such as paper or the like, utilizes so-called "data strips". In essence, a data strip consists of a series of rows of printed bit-mapped data patterns that fills a given two-dimensional rectangular area on a piece of paper. Each row contains a ordered co-lineal arrangement of relatively small essentially square white and black bits that extends across the length of that row. Each bit may occupy several adjacent pixels. The ordering of the bits in each row determines the digital data stored therein. A white bit is associated with one binary state; a black bit is associated with the other binary state. The data collectively stored within all the rows defines the data contained within the entire strip. To read a strip, a user passes a hand scanner or scanning wand, typically employing a line scanner, along one direction, e.g. the horizontal direction, across the strip to simultaneously read a column of pixels that extends vertically throughout the width of the strip. As the conclusion of this pass, all the pixels in all the rows have been scanned a column at a time.
For a fixed size strip, as the size of each bit in this strip decreases, the amount of data contained within each row increases as does the number of rows that can occupy the entire strip. As such, the data capacity of the strip correspondingly increases.
Inasmuch as a data strip can be accurately imprinted on nearly any flat substrate, regardless of whether it is magnetic or not, data strips show great promise in providing an auxiliary on-film digital data store for use in conjunction with human readable microfilm images. To provide sufficient longevity, a data strip for microfilm applications might likely be first printed on paper or a suitable media and then be photographically reduced along with a corresponding page of a document onto microfilm. The reduced image of the strip would be located in the vicinity, typically above or below, the reduced image of the page. In this case, since the documentary page and the strip are both photographically stored within the microfilm, the microfilm would provide the same long term integrity for both the microfilmed strip and the microfilmed document page.
A data strip that would be suitable for use in a microfilm application would likely be quite small. In this regard, each separate pixel would measure approximately 0.08 mills (approximately 2 .mu.m) on each side such that, after magnification, pixels of this size would provide a resolution of approximately 400 dots/inch (approximately 158 dots/centimeter--cm). At this resolution, a bit on the microfilm would be formed of a block of vertically and horizontally adjacent pixels and could consume approximately 9 .mu.m.sup.2 of film area. With this size, a photographically reduced data strip of approximately 6 mm by 2 mm (approximately 0.24 by 0.08 inches) should be able to hold 50-100 bytes of data in each row and approximately 20 Kbytes in the entire strip, which is sufficient to accommodate approximately 10 pages of ASCII data and more using suitable compression techniques. Accordingly, such a data strip can store a reasonable amount of digital information in a relatively small physical space.
One attempt in the art for providing a data strip, though suited for use with paper media, is described in, for example, U.S. Pat. Nos. 4,782,221 (issued to R. L. Brass et al on Nov. 1, 1988); 4,754,127 (issued to R. L. Brass et al on June 28, 1988) and 4,728,783 (issued to R. L. Brass et al on Mar. 1, 1988). Here, data strips are used to store computer programs and/or data on paper and are scanned by use of a hand scanner or scanning wand. While the strips described in these patents (commonly and hereinafter referred to as "Cauzin" strips) do provide a paper-based digital data store, these strips suffer serious drawbacks which prevents their usage on microfilm media. First, tracking errors, often substantial, can occur between the axial orientation of a hand scanner and the orthogonal rows and columns of bits in a Cauzin strip. As such, in an effort to compensate for these errors, the data recorded in Cauzin strips generally contains strong redundancies as well as embedded synchronization and/or tracking bits (collectively referred to as "clock bits"). Unfortunately, by embedding numerous clock bits directly within each row, the amount of digital data that can be stored within that row significantly decreases thereby seriously and adversely affecting the data capacity of the entire strip. Second, the algorithms that are currently used to extract data from a Cauzin strip greatly restrict the physical size of each bit on the strip. Accordingly, if the bit size were to markedly decrease from one Cauzin strip to another, a scanner that could read the former strip would not likely be able to read the latter strip. While this limitation is generally of little consequence for paper based strips--inasmuch as the lifetime of these strips is expected to be very short perhaps a few weeks or months such as where a Cauzin strip is printed on a page of a popular monthly or bi-weekly consumer computer magazine, this limitation can not be tolerated with data strips recorded on microfilm where the longevity of the media is substantially longer, often measured in decades. Specifically, over the past few years and into the future, the resolution of line scanners; particularly charge coupled device (CCD) scanners, has an will continue to significantly increase as the size of each CCD cell used in a line scanner continues to shrink. Hence, data strips recorded on microfilm at one resolution must be capable of being read by a line scanner operating at a higher resolution. Otherwise, the utility of a microfilmed image would be limited, not by the substantial longevity of the underlying microfilm media itself, but unfortunately by a much shorter time interval required for each successive evolution of line scanners offering an increased resolution to become commercially available in the art. Accordingly, Cauzine strips appear to be highly impractical for use with microfilm images.
Furthermore, horizontal and vertical skew (rotational mis-alignment) can arise in a data strip recorded on microfilm while it is being read by a microfilm line scanner. This skew manifests itself as a rotational mis-alignment occurring between the orientation of the orthogonal components, e.g. rows and columns, of the data strip itself and the scanning axis of the scanner. If this skew is not taken into account while the strip is being read, then erroneous points on the data strip will be sampled that, depending upon the amount of actual skew that occurs, could produce significant data errors. This skew can arise for a variety of reasons. First, skew can illustratively occur because the axes of the data strip itself were not properly oriented with respect to the axes of the microfilm while the strip was being photographed onto the film--i.e. such that the orthogonal axes of the strip as it appears on the film are not are exactly parallel to corresponding orthogonal axes of the microfilm. Second, slight differential slip that can occur across the width of the film as it moves through a film transport past a read head can introduce skew between the line scanner and a data strip recorded on the film. For whatever reason skew occurs, this skew must be compensated during a read process.
Therefore, a specific need also exists in the art for a technique for use in properly extracting data from a microfilm data strip. This technique should properly extract data from the strip essentially independent of bit size. In addition, this technique, should not require embedding numerous clock bits within the data itself recorded on each row of the strip. Furthermore, this technique should be sufficiently robust to accurately compensate for skew that is likely to occur in reading a microfilmed data strip by a line scanner existing in a microfilm reader. By meeting this specific need, machine readable microfilmed digital data strips can be used along with associated human readable microfilm images co-existing therewith on common microfilm media in order to provide an inexpensive combined microfilm data and image storage system.